Need a thin power supply: 110v AC adapter to 12v 1a. Can I use a 110 USB 5v 1a instead?

I am in need of a slim adapter, the current one I have is 1.2" in depth/thickness I need to be closer to 1".

I'm trying to power power a small micro controller + DC pump 4.5watts at 12v dc.

The adapter I'm using now is 12v 1a 12w to a standard 5.5mm/2.1mm barrel plug.

I can't seem to find an smaller form factor wall wart that matches those specs.

What I can find are incredibly slim USB wall adapters but they're all rated at 5v. And I can find USB to 5.5 mm/2.1 barrel plugs.

The ultimate question is can I use a USB adapter with at least the same wattage and amperage but a lower voltage for my system.

Or could I use something like these two in combination?

It can be done in a convoluted and inefficient way.
You would have to have at the load side a 5 to 12 volt boost converter.

You need 12V unless you can find a 5V pump.

Chaostactics said:

Or could I use something like these two in combination?

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That should work. The power rating of the wall charger and the power rating of the 5 V to 12 V adaptor must both be larger than the power rating of the water pump.

It is a convoluted way of doing it, but it uses cheap, off the shelf components and it should work, so it is probably the best solution. I would not advise trying to make something that fitted into a 1" gap and works with mains voltage. That is very difficult.

I wouldn't worry about the fact that you are converting voltages twice. When someone plugs an inverter into the 12 V accessory socket in an electric car, and runs a laptop from that, which happens all the time, the power conversion path is really complicated. It's something like this:-

DC-DC converter in car
400 V dc -> inverter -> 400 V ac (high frequency)
400 V ac -> transformer -> 12 V ac
12 V ac -> rectifier -> 12 V dc

Plug-in inverter
12 V dc -> inverter -> 12 V ac (high frequency)
12 V ac -> transformer -> 180V ac (high frequency)
180 V ac -> rectifier-> 180 V dc
180 V ac -> inverter -> 120 V ac (60 Hz)

Laptop power supply
120 V ac -> rectifier -> 180 V dc
180 V dc-> inverter -> 180 V ac (high frequency)
180 V ac -> transformer -> 20 V ac
20 V ac -> rectifier -> 20 V dc for laptop

And then the laptop will do further voltage conversions because it will charge its battery at some lower voltage, and the electronics will run from a variety of other voltages.

It is really complicated, and of course it could be simplified, but the components used are there anyhow, or are cheap and readily available. The DC-DC converter comes in the car, because most of the electronics in an electric car come from combustion engine cars with 12 V supplies, and you wouldn't want 400 V supplies going everywhere in a car anyhow. The laptop power supply comes with a laptop to run it from the house outlets. The plug in-inverter is useful for lots of things in cars whether or not the car has a 400 V traction battery, so it is a mass-produced, cheap device.

I don't know of any slimline wall wart style, but could you use a "brick" type with a trailing power cable, just swapping the power plug or cable to a right-angle one to keep the depth down?

You have a separate item in a cable as you would using a 5V unit and separate voltage converter, but it's ready built, fully insulated and ready to use.

eg. This one is a bit higher current that you need, but that should not matter, it will just run cooler and should have a longer life:

There are plenty of others that could be suitable.

Example low profile plug power cable that should fit the above brick:

Again, there are many types and lengths available.